Intermediate spin pair relaxation through modulation of isotropic hyperfine interaction in frequency-swept spin-dependent recombination in 4H-SiC

Electrically detected magnetic resonance (EDMR) measurements have been extended to sub-mT magnetic fields through utilization of frequency sweeping of the oscillating magnetic field, where conventional electron paramagnetic resonance-based measurements traditionally utilize magnetic field magnitude ramping. In spin-dependent transport measurements in devices, an oftentimes pervasive near-zero field magnetoresistance effect overwhelms the sub-mT regime. This magnetoresistance effect is independent of the RF drive. Thus, by utilizing a constant DC magnetic field and a frequency sweep of the RF magnetic field, the magnetoresistance effect is not detected, leaving only the EDMR response. Interesting EDMR-based phenomena emerge at sub-mT fields when the oscillating field magnitude approaches the static field, such as multiple-photon transitions caused by the emergence of Floquet spin states and Bloch-Siegert shifts. A spectral-narrowing effect also emerges as the static field is reduced. In this work, we show that the narrowing of the frequency-swept EDMR response with static field can be modeled by changes in intermediate spin-pair relaxation through modulation of hyperfine fields caused by stochastic perturbations from the environment. We utilize recently developed theory to model the relaxation of spin pairs and show that stochastic interactions of the electron spin with the environment yield both Floquet spin states and changes in intermediate spin-pair relaxation.